Potters Bar becoming part of zone 6 or zone 7 would make sense, but I wonder if Hatfield and WGC (and indeed St Albans) would become part of the zones?
If not, they're going to end up being special zones, like Broxbourne, which then gives a problem as they're running out of zones/letters.
Should do Zones 8-10 rather than outside, something I feel should be the case with the Tattenham Corner branches that should be part in Z7 rather than 6
